Heart rate and respiratory monitor

ABSTRACT

Apparatus for detection of pulse repetition rate and oxygenation of blood flow, comprising a solid state probe having a narrow bandwidth light source housed to direct light upon a patient&#39;&#39;s finger and a photodetector housed for receiving reflected light from such finger, the output of the detector being connected to electronic circuitry for detecting pulse repetition rate of blood flow and for detecting signal level representative of the degree of oxygenation of the patient&#39;&#39;s blood. The use of a low power narrow bandwidth light source with a red emission characteristic permits precise detection of the degree of oxygenation of the blood.

D United States Patent 1151 3,704,706 Herczfeld et al. 1 Dec. 5, 1972[541 HEART RATE AND RESPIRATORY 3,228,391 1/1966 Fitter et a1...128/2.05 T

MONITOR 3,230,951 1/1966 Teschner ....128/2.05 P [72] Inventors: BonitaFalkner Herczfeld; Peter R 3,511,227 5/1970 Johnson ..l28/2.05 F

of Philadelphia Pad FOREIGN PATENTS OR APPLICATIONS Richard D. Klaiter,Willingboro, NJ. 987,504 3/1965 Great Britain .128/2.05 P [73] Assignee:Drexel University, Philadelphia, Pa. Primary Examiner Richard Gaudet[22] Filed; O t, 23, 1969 Assistant Examiner-Kyle L. Howell At P 1 [211Appl. No.: 868,823 and Paul [57] ABSTRACT [52] "128/2 128/205 2Apparatus for detection of pulse repetition rate and [5] 1 1m Cl 54oxygenation of blood flow, comprising a solid state a I u 1 6 6 1 u l 6u v 6 a s u s I n 6 n 6 I n 6 n 6 6 n 6 6 I 6 ll a [58] held of Searchto direct light upon a patients finger and a photodetector housed forreceiving reflected light from such finger, the output of the detectorbeing connected to [56] References cued electronic circuitry fordetecting pulse repetition rate UNITED STATES PATENTS of blood flow andfor detecting signal level representame of the degree of oxygenauon ofthe patlents 2,640,389 6/1953 L1ston ..128/2 R blood The use of a lowpower nan-ow bandwidth light M03214 9/1963 Smth P source with a redemission characteristic permits 31121066 3/1964 Brumley "128/2 R precisedetection of the degree of oxygenation of the 3,139,086 6/1964 Botschetal ....12s/2.05 P blood. 3,152,587 10/1964 Ullrich et al. ..l28/2 R3,167,658 1/1965 Richter ..128/2.05 P gga i nsyt Drawing Eigures 9 POWERSUPPLY 4Q i 1 1 A BUFFER VOLTMETER- DETECTPR AMPLIFIER l 52 l i 29 3O 2731 I 26 I l 1 I 1 g SCHMITT MONOSTAB LE PROBE i AMPLIFIER TRIGGER MV.DRIVER I R L .i

r r PATIENT g fis PATENTEDnEc 5 I972 3704.706

SHEET 2 OF 2 NORMAL PROBE OUTPUT VOLTAGE RESPIRATORY DISTRESS SCHM lTTTRIGGER MULTIVIBRATOR INVENTORS.

BONITA FALKNER HERCZFELD PETER R. HERCZFELD RICHARD D. KLAFTERATTORNEYS.

HEART RATE AND RESPIRATORY MONITOR BACKGROUND OF THE INVENTION A. Fieldof the Invention This invention lies in the field of heart rate monitorsand, more particularly, solid state monitors for detection of peripheralflow and oxygenation of blood in a newborn infant patient.

B. Description of the Prior Art The problem of accurately monitoring theheartbeat and of obtaining information regarding the flow of oxygenatedblood in a newborn infant has long resisted the development of aneconomical instrument. The severity of the problem is based on themedical consideration that an infant, and particularly a prematureinfant, when undergoing an exchange blood transfusion, sometimes sufferscardiac arrest which, if undetected for a relatively short period oftime, may cause permanent brain damage or death. Further, physicians arevitally interested in obtaining information relating to respiratoryarrest and the degree of oxygenation of the blood being circulatedthroughout the body during and after an exchange transfusion. It is ofparticular importance to have information which discloses a partialcardiac arrest or a partial respiratory arrest, so that the physiciancan take swift action to alleviate and correct the situation. There isthus a requirement for continuous monitoring of both pulse repetitionrate, a change in which often precedes cardiac arrest, and the level ofoxygen in the blood, which is an indication of respiratory distress.

The prior art shows a number of heart monitoring devices. However, mostof these devices are designed for clinical use on adults and aregenerally not suitable for use with newborn infants. Particularly,devices utilizing electrodes generally require that the electrodes be ofa sufficient size to pick up the extremely small biopotential signalswhich are monitored, such large electrode sizes being unworkable fornewborn infants. Furthermore, commercially available heart monitoringdevices are extremely expensive, and provide no information about theflow of oxygenated blood.

Apparatus for the measurement of peripheral pulsations has a number ofdistinct advantages over the electrocardiogram and other similardevices. First, it is known that it is possible for electrical activityof the heart to persist after the heart has actually stopped beating.Thus, a monitor designed to detect biopotentials could be late indetecting any cardiac arrest. Further, it is extremely difficult toplace electrodes on infants in such a way as to avoid extraneous noisepickup. And, perhaps most importantly, a monitor that only sensesbiopotentials cannot detect respiratory distress.

Digital monitors, or transducers, for detecting peripheral pulsations,and utilizing a light source in combination with a detector, have beenshown in the art. More particularly, the prior art discloses a digitaltransducer comprising a light source in combination with a photoelectriccell, with a red filter placed over the photoelectric cell. Since thephotocell is responsive to light in the red region of the spectrum,arterial pulsations which drive blood into the digit result in anincreased redness and increased photocell response, thus giving anindication of the pulse repetition rate. However, a bulb and filtercombination is inefficient, most of the radiated energy being outside ofthe red. Only by inclusion of a prohibitively expensive optical filtercould such a light and filter combination produce a narrow band width onthe order of that provided by a laser. In addition to being morecumbersome, the device necessarily has a heating problem, which makes itparticularly undesirable for use with infants. Further, the devicedetects only volume of blood flow, and cannot distinguish between bloodvolume and degree of oxygenatlon.

SUMMARY OF THE INVENTION The primary object of this invention is toprovide apparatus for the detection of oxygenated blood flow which issimple, efficient, lightweight, inexpensive and effective for thepurpose and which overcomes the disadvantages of the prior art.

It is a further object of this invention to provide a heart rate monitorcomprising a solid state optical probe which is suitable for use onpremature infants, and which senses peripheral pulsations of the heart.

It is a further object of this invention to provide apparatus whichmonitors both heart pulse rate and oxygenation of blood flow.

Accordingly, this invention provides apparatus comprising a solid statelaser as a source of light in combination with a solid statephotodetector, forming an optical probe suitable for sensing peripheralpulsations of the heart. The solid state laser is a very small andextremly efficient light source emitting microwatts of power in a narrowband width having peak emission occurring in the red range of theoptical spectrum. The laser directs a low energy beam of light at thecapillaries of a finger, the blood flowing within reflecting incidentred light which is detected by a photodetector housed adjacent to thelaser and having a response curve suitable for detection throughout theemission spectrum of the laser. The electrical output of the probe istransmitted to processing apparatus having pulse detection circuitry todetermine the pulse repetition rate, as well as DC level detectioncircuitry to determine the relative oxygen content of the blood.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a schematic diagram ofthe probe housing and its elements in relation to a patients finger.

FIG. 2 shows a schematic diagram ofan alternate construction of theprobe housing.

FIG. 3 shows a block diagram of electronic processing circuitry which isconnected to the probe.

FIG. 4 shows a representation of waveforms produced by the probe andelectronic processing circuitry.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings,FIG. 1 shows a schematic diagram of the probe and its elements. Theprobe 20 is placed on the patients finger by conventional strapping ortape and aligned such that the light source 21 directs incident light,indicated by arrows marked I, at the patients finger. The detector 22 isplaced adjacent to light source 21 and disposed in order to collectreflected light, indicated by arrows marked R,

106009 OIBS from the patient's finger. The light source 21 andphotodetector 22, combined with housing 23, form the probe 20, which hastypical overall dimensions of xi; inch X V4 inch X V4 inch. The lightsource 21 is suitably a gallium arsenide solid state laser which itselfis onetenth inch in diameter and 0.15 inch in length, having typically25 microwatts of power being emitted in a narrow band width with thepeak emission occurring at 6,700 angstrom, i.e., in the red range of thecolor spectrum. Such a typical gallium arsenide laser is commerciallyavailable. See, for instance, Monsanto model MV 1 A. The photodetector22 is required to have high sensitivity through the frequencies of theemission spectrum of the laser. A suitable photodetector is the MotorolaMRD2 50 volt NPN silicon photodetector. This detector is approximately0.06 inch in diameter and a maximum of 0.! 18 inch in height, whichdimensions permit incorporation into the 5% inch X l4 inch X A inchprobe device. A photodetector having frequency selectivity matching thelaser characteristics would further increase the selectivity of theprobe.

The probe housing 23 may be fabricated from a piece of metal, suitablybrass, having parallel recesses or holes 25 drilled within it toaccommodate the laser and photodetector respectively, the holes beingoriented perpendicular to the probes surface which is placed against thefinger. Between recesses 25 is an insulating member 26 which opticallyisolates the recesses, thereby optically isolating the laser andphotodetector. Alternately, the probe housing may be made from anepitaxial plastic, as shown in FIG. 2. A front portion 27 of a clearnonhardening plastic may be added, thereby encapsulating the laser andphotodetector without significantly impeding light transmission. A powersupply 39 provides power for the laser and the photodetector, as well asthe electronic circuitry described hereinbelow.

In operation, the probe is placed upon the patients finger such thatblood which is flowing in the capillaries of the finger reflectsincident red light. The intensity of the reflected light is proportionalboth to the amount of blood flowing in the finger and to the freshnessof the blood, i.e., the degree to which it is oxygenated. For eachheartbeat, fresh blood is pumped into the capillaries, thereby causing aperiodic increase and decrease in the reflected light intensity. Undernormal conditions then, a periodic waveform such as shown in FIG. 4awill be detected, which waveform represents both volume and color of thecirculating blood. The waveform has an AC component corresponding to theheart pulsations, and a DC component which will be directly proportionalto the redness, or oxygenation, of the blood. In the event of partialcardiac arrest, the pulsations vary in frequency, which condition can beeasily detected. When a respiratory distress occurs, the heart continuesto pump blood, but it is relatively unoxygenated blood with acharacteristic bluish hue. Since the probe is relatively insensitive inthe blue region of the light spectrum, such a respiratory distress isimmediately manifested by a probe signal of diminished amplitude, asshown in FIG. 4b. By contrast, in the partial cardiac arrest condition,the pulse repetition rate will change, while the amplitude and DC levelwill remain essentially the same. To distinguish the respiratorydistress condition from the partial cardiac arrest condition, the DCcomponent of the signal, or the peak-to-peak value, is monitored. Thus,by distinguishing pulse repetition rate and DC level, the two cases canbe separately diagnosed.

Referring now to FIG. 3, a block diagram of the heart rate andrespiratory monitor is shown. The signal developed by the probe 20, asshown in FIG. 4a, is coupled into electronic circuitry 40 forinformation processing. The signal is first fed through a conventionalsolid state DC amplifier 25 which amplifies the total signal. The outputof amplifier 25 is parallel coupled to a conventional Schmitt Triggercircuit 26 and to a detector 29. The Schmitt Trigger 26 is a bistableelectronic device which, when driven by the pulsating signal, willswitch between two stable states, thus producing a squarewave output asshown in FIG. 4c. Such squarewave may suitably be differentiated andapplied to a conventional mono-stable multivibrator 27, whichmultivibrator will produce a pulse train output having suitable pulsewidths, and having a pulse repetition rate equal to that of the probewaveform. Such a mono-stable output is shown in FIG. 4d. This output,then, can be coupled to a conventional driver circuit 31, such as anemitter follower, which in turn drives a suitable monitoring device 28,such as a beep tone generator or oscillograph.

Still referring to FIG. 3, the output of amplifier 25 is also fed into adetector 29, suitably a conventional DC detector. The output of detector29 is coupled, preferably through a buffer amplifier 30, to a suitablevolt meter 32 which would indicate the magnitude of the detected DCvoltage. The volt meter 32 can be suitably equipped with a referenceneedle, which needle can be set at a lower limit, such that when the DClevel drops to such lower limit, the meter would sound an alarm signal,notifying a physician. By checking the pulse rate output, the physiciancould immediately determine whether the drop in DC level was due to arespiratory or cardiac cause.

It is to be understood that detector 29 could, alternately, be apeak-to-peak detector of conventional circuitry, and be connected to apeak-to-peak volt meter which would indicate the magnitude of thedetected voltage pulses in the signal from probe 20. Either the DC levelor the peak-topeak information, when compared with the pulse repetitionrate, would be sufficient to enable the physician to distinguish betweencardiac arrest and respiratory distress.

From the foregoing, it is seen that this invention provides an extremelyefficient and suitably small device for monitoring blood flowcharacteristics of an infant. The choice of a laser which producesapproximately 25 microwatts makes possible a very cool and efficientdevice. Further, by using a narrow beam laser, it is possible to producea device which is very sensitive to changes in blood color. By contrast,apparatus utilizing white light in combination with a red filter, inaddition to being inefficient and generating heat which would beprohibitive in clinical uses with infants, produces a relatively broadrange of red light. Consequently, relatively large changes in oxygencontent must take place before detection by a white light and filtercombination, whereas extremely small changes can be detected with thefrequency selective laser probe of this invention.

IOGDOQ 0186 It is to be noted that equivalent narrow beam light sourcesincluding light-emitting diodes, whether the light is coherent or notmay be utilized in place of lasers in the practice of this invention. Itis further noted that while specific electronic circuitry for processingthe probe signal has been discussed in this specification, a widevariety of pulse repetition rate and level detection circuits can beused.

We claim:

1. Heart rate and respiratory monitor apparatus for detecting pulserepetition rate and oxygenation of blood flow in a patient, comprising:

a. a probe housing having first and second light transmitting faces;

b. a low power solid state laser red light source, having narrowbandwidth emission characteristics, positioned in said probe housing toemit red light through said first face;

c. semiconductor photodetector means for detecting red light reflectedthereon, said photodetector means positioned in said housing to receivelight through said second face of said housing, such that when saidfaces of said probe housing are positioned contiguous to a periphery ofa patient, incident light from said red light source is reflected fromsuch periphery and received by said photodetector means;

d. electronic processing means connected to said photodetector meanshaving pulse repetition rate circuitry and first output means coupledthereto for monitoring said patients pulse repetition rate, and signallevel detection circuitry and second output means coupled thereto formonitoring the degree of oxygenation of said patients blood; and

e. a power source connected to and supplying energy to said red lightsource, said photodetector means, and said electronic processing means.

2. Heart rate and respiratory apparatus for detecting the pulserepetition rate and degree of oxygenation of blood flowing in aperipheral portion of a patient, comprising: i

a. narrow bandwidth red light means for transmitting incident red lightupon said peripheral portion and detecting red light reflectedtherefrom;

b. a probe housing means for housing said red light means such that,when positioned contiguous to said periphery, some of said incidentlight is reflected from the blood flowing in said periphery and receivedby said reflecting means; and

c. electronic processing means connected to said detecting means fortransforming said reflected red light into an electrical signalrepresenting said reflected red light, and including pulse repetitionrate circuitry for monitoring said patients pulse repetition rate, andsignal level detection circuitry for monitoring the degree ofoxygenation of said patients blood, said red light means including anarrow bandwidth solid state laser mounted within said probe housingmeans to direct incident red light to said periphery, and asemiconductor photodetector mounted in said probe housing means toreceive red light reflected from said periphery.

1. Heart rate and respiratory monitor apparatus for detecting pulserepetition rate and oxygenation of blood flow in a patient, comprising:a. a probe housing having first and second light transmitting faces; b.a low power solid state laser red light source, having narrow bandwidthemission characteristics, positioned in said probe housing to emit redlight through said first face; c. semiconductor photodetector means fordetecting red light reflected thereon, said photodetector meanspositioned in said housing to receive light through said second face ofsaid housing, such that when said faces of said probe housing aRepositioned contiguous to a periphery of a patient, incident light fromsaid red light source is reflected from such periphery and received bysaid photodetector means; d. electronic processing means connected tosaid photodetector means having pulse repetition rate circuitry andfirst output means coupled thereto for monitoring said patient''s pulserepetition rate, and signal level detection circuitry and second outputmeans coupled thereto for monitoring the degree of oxygenation of saidpatient''s blood; and e. a power source connected to and supplyingenergy to said red light source, said photodetector means, and saidelectronic processing means.
 2. Heart rate and respiratory apparatus fordetecting the pulse repetition rate and degree of oxygenation of bloodflowing in a peripheral portion of a patient, comprising: a. narrowbandwidth red light means for transmitting incident red light upon saidperipheral portion and detecting red light reflected therefrom; b. aprobe housing means for housing said red light means such that, whenpositioned contiguous to said periphery, some of said incident light isreflected from the blood flowing in said periphery and received by saidreflecting means; and c. electronic processing means connected to saiddetecting means for transforming said reflected red light into anelectrical signal representing said reflected red light, and includingpulse repetition rate circuitry for monitoring said patient''s pulserepetition rate, and signal level detection circuitry for monitoring thedegree of oxygenation of said patient''s blood, said red light meansincluding a narrow bandwidth solid state laser mounted within said probehousing means to direct incident red light to said periphery, and asemiconductor photodetector mounted in said probe housing means toreceive red light reflected from said periphery.